Some Roman Emperors violated tradition and died peacefully in their beds. Most, however, met violent ends, particularly in last two centuries of the empire in the West. Josh Fruhlinger, once a graduate student in ancient history, has sorted all of the Western emperors by the brutality of their deaths. The #1 position goes to Valerian (r. 253-260), the only Emperor to become a prisoner of war. The Persians were not kind:

Captured by the Persians and died in captivity; rumored to have been used as a human footstool by the Persian king, killed by having molten gold poured down his throat, then taxidermied.